1. Field of the Invention
The present invention relates to a magnetic disk cartridge, and more particularly, to an improved provisional assembly structure for the cassette shell halves of a magnetic disk cartridge having a rotatable magnetic disk encased in a cassette shell constituted by mating and joining a pair of cassette shell halves.
2. Description of the Related Art
A magnetic disk cartridge comprises a magnetic disk for magnetically recording analog and/or digital signals rotatably encased in a thin cassette shell. The cassette shell is formed in the shape of a flat prism with a rectangular top surface slightly larger than the magnetic disk, a bottom surface having an opening through which a center core supporting the center of the magnetic disk is exposed and narrow side surfaces extending between the outer peripheral edges of the top and bottom surfaces. The magnetic disk cartridge is provided with a magnetic head access opening for insertion/withdrawal of magnetic heads used for magnetic recording and reproducing so as to enable the magnetic heads to be brought into contact with, or close to, the opposite surfaces of the magnetic disk from the exterior. The magnetic head access opening is equipped with a shutter for preventing invasion of dust and the like when the magnetic disk cartridge is not in use. Liners made of nonwoven fabric or the like are attached to the inner surfaces of the cassette shell opposite the main surfaces of the magnetic disk for protecting the surfaces of the magnetic disk from scratching as well as for wiping off dust and the like adhering thereto.
The space inside the cassette shell of the conventional magnetic disk cartridge is fairly large in the direction of magnetic disk thickness and the liners are accommodated in the spaces remaining above and below magnetic disk. Each liner is urged away from the inner surface of the cassette shell and maintained in contact with the corresponding surface of the magnetic disk by a weak plate spring called a lifter. Owing to this arrangement, a certain degree of tolerance is available regarding the dimensional precision of the cassette shell in the thickness direction.
In recent years, new high-density recording methods have led to the development of a magnetic disk cartridge with 50 times the capacity of the widely used conventional magnetic disk cartridge (3.5-inch floppy disk). The magnetic disk of this type of magnetic disk cartridge is rotated at a much faster speed than the conventional one and the magnetic heads used for recording and reproducing signals to/from the magnetic disk are required to be positioned with very high precision.
A quality inspection is conducted as the final step in the assembly of magnetic disk cartridges and a cartridge found to be defective is removed from the line as a reject. Various types of defects may occur. When the defect is in the magnetic disk, not the cassette shell halves, it is preferable for the cassette shell halves to be reusable since they are precision molded and therefore expensive to produce.
The magnetic disk cartridge comprises a pair of mated and joined cassette shell halves and the magnetic disk is encased by the cassette shell halves to be rotatable therein. Thus, if the quality inspection is conducted before the cassette shell halves encasing the magnetic disk are permanently joined by ultrasonic welding or the,like in the final assembly step, a magnetic disk found to be defective can be replaced and the cassette shell halves be reused.
It is therefore preferable to adopt a structure which, in the final assembly step, allows the cassette shell halves to be provisionally assembled after the magnetic disk has been accommodated therein and the quality inspection to be conducted before permanent assembly by welding or the like so that the cassette shell halves can be readily disassembled if the magnetic disk is defective.
Although a provisional assembly structure employing screw fastening has been adopted in conventional audio and video cassettes, screw fastening limits the number of reuses possible because the tapped hole receiving the screw wears with repeated screw fastening. In addition, the screw fastening and screw removal operations are inefficient because each screw has to be turned independently with a screwdriver.
A method of provisionally assembling the cassette shell halves by inserting engaging pins provided on one cassette shell half into engaging holes provided in the other was therefore proposed. Since this method requires a certain amount of play to be established between the engagement pins and the engagement holes, however, some of the resulting provisionally assembled cassette shells turn out to have a loose fit between the cassette shell halves. A thorough quality inspection of a provisionally assembled magnetic disk cartridge with loosely fitted cassette shell halves has been found to be impossible owing to the difficulty of rotating its disk at a high speed.